One method to control intake and exhaust valve operation during engine operation is described in U.S. Pat. No. 6,374,813. This method presents a means to control electromagnetically actuated valves to promote EGR control. The approach selects different valve modes and patterns to regulate internal EGR, i.e., EGR flow through a cylinder as opposed to EGR routed to the intake manifold. Valves are operated independently and control is based on operating conditions of the engine. Further, the disclosure also describes several valve configurations that may be operated in one or more operational modes to promote cylinder air charge swirl.
The above-mentioned method can also have a disadvantage. Specifically, the approach may degrade engine breathing for engines that have different length intake runners. For example, some engines have two intake runners per cylinder, a long runner and a short runner; where the unequal length intake runners are selectively used to improve engine performance at different engine operating points. However, since the before-mentioned approach simply selects valves based on a desired amount of EGR without regard to the intake manifold geometry, engine breathing may degrade.
Further, if the valves are operated as suggested, it may be possible for early valve degradation to occur due to high temperature valve operation, since valve selection is based simply on a desired amount of EGR.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method of electromechanical valve control that offers substantial improvements.